In the field of medical diagnosis and graphic arts, there have been concerns in processing of photographic film with respect to effluent produced from wet-processing of image forming materials, and recently, reduction of the processing effluent is strongly demanded in terms of environmental protection and space saving. Silver salt photothermographic dry imaging materials forming images only by application of heat have been put into practical use and spread rapidly in the foregoing fields.
Silver salt photothermographic dry imaging materials (hereinafter, also denoted as thermally developable photothermographic materials or simply as photothermographic materials) have been proposed so far, as described in U.S. Pat. Nos. 3,152,904 and 3,487,075; D. Morgan, Dry Silver Photographic Material; and D. H. Klosterboer, “Thermally Processed Silver Systems” in IMAGING PROCESSES and MATERIALS, Neblette's Eighth Edition, edited by J. M. Sturge, V. Walworth, and A. Shepp (1969) page 279.
Photothermographic materials are processed using a thermally processing apparatus, usually called a thermal processor, which uniformly heats photothermographic material to form images. Such thermal processors are readily available in the market along with the recent spread thereof.
Recently, more downsizing of laser imagers and more rapid access thereof are further desired. There have been proposed various processing techniques, including a method of rotating a heated drum while bringing a photothermographic material into contact with the drum surface, a method of transporting a photothermographic material while pressing the photothermographic material onto the surface of a pre-heater and compressing it with a roller and a method of inserting a photothermographic material between plural roller pairs to transport it while allowing the rollers to rotate to perform thermal development. However, either one of the foregoing methods is easily influenced by fluctuation in temperature of the thermal developing section, producing problems such as unevenness in development and transportation troubles.
Performing thermal development at high temperatures of 100° C. or more results in highly heated photothermographic material immediately after completion of thermal processing, so that it is important to cool it down at a high speed to achieve rapid access. To overcome such problems, JP-A (hereinafter, the term, JP-A refers to a Japanese Patent Application publication) 3-208048 disclosed a method for cooling. However, such a method resulted in problems such as marked unevenness in density or transportation troubles, markedly vitiating commercial values. It was further proved that aging change of density increased due to differences in cooling process after processing.